A. Field of the Invention
This invention relates generally to the subject of three-dimensional scanners, for example those based on projection of a two-dimensional coded pattern off of a surface and capture of the reflected pattern. More particularly, the invention relates a method of scanning an object in a “wet-field” environment, that is, where the object to be scanned is moist with water or saliva. One example is oral structures, such as teeth, lips and gingival tissue, in a human patient. The method involves applying a composition of matter to the surface that improves the reflective properties of the object and temporarily resists being washed away from the surface due to the presence of water, saliva, or other moisture.
B. Description of Related Art
Three-dimensional scanners for scanning of teeth (either directly or from a model) are known in the art and described in the patent literature. See the published PCT patent application of OraMetrix, Inc., publication no. WO 01/80761, the entire contents of which are incorporated by reference. See also Rekow, et al., U.S. Pat. No. 5,027,281, Massen et al., U.S. Pat. No. 5,372,502 and Brandestini et al., U.S. Pat. No. 4,837,732.
The scanner of WO 01/80761 uses a coded projection pattern consisting of a two dimensional array of lines and colored dots. The pattern is projected onto the surface to be scanned. The pattern is reflected off of the surface and imaged by a two dimensional charge coupled device (CCD) chip. The location of where the various portions of the projected pattern is imaged by the CCD chip contains information as to the three-dimensional location of the points on the object's surface corresponding to points in the reflected pattern. An algorithm derives 3D location information for all the available points in the reflected projected pattern, thus deriving 3D information as to the surface being scanned.
Some surfaces have an inherent reflectivity such that the projected pattern from a scanner such as described in WO 01/80761 will reflect the projected pattern onto the imaging device to a satisfactory degree without any prior preparation of the surface. Other surfaces are relatively non-reflective or translucent, or otherwise do not reflect the projected pattern to a sufficient degree. For such surfaces, the scanning of the object can be improved by applying a substance to the object to improve its reflective properties. The CEREC scanning device developed by Brandestini et al. is used in conjunction with a TiO2-based aerosol powder which is applied to the teeth.
When the object is being scanned is the teeth, lips, or other oral structures of a human patient, particular problems arise that have not been satisfactorily addressed by the prior art. For example, the TiO2-based aerosol powder used in the CEREC system tended to form small globules on the surface of the teeth, which interferes with obtaining accurate 3D surface information. The formulation was readily washed away by saliva. It did not adhere well to the tooth surface. Moreover, the powder was also quite technique sensitive and difficult to apply evenly, in that the ability to apply the power evenly and spread it over the entire surface of the tooth was dependent to a large degree on the skill of the operator. While the powder could be used by a very skilled operator for very limited scanning of a single tooth (with adequate saliva-absorbing material completely surrounding the tooth) in a dry field environment, it is completely inadequate for scanning a set of teeth or an entire jaw, a situation in which the required dryness cannot be practically achieved in any convenient fashion.